Variable automatic clearance pocket



Oct. 9, 1951 Q MEYERS 2,570,965

VARIABLE AUTOMATIC CLEARANCE POCKET Filed Dec. 19, 1946 COMPRESSED GASCONTROL SECTlON PULSATION DAMPENER GAS TO BE PRESSED PRESSOR INTAKECOMPRESSOR CYLINDER COMPRESSOR DISCHARGE /NVENTOR C4 0. MEYERS ATTORNFYSPatented Oct. 9, 1951 VARIABLEAUTOMATIC CLEARANCE PUCKET) Charles.Myers;.-Bartlesville, -Okla.,.,assignor to Phillips Petroleum Company,a .corppration of Delaware ApplicationDecember-P19, 1946;21S'erialN0;-'-.7-17;263:

Claims.

This invention relates. ta reciprocating vcome pressors. In. one. ofitsimoreespecific aspectssit relates. to a. variable. automaticclearance. pocket. for useewith' reciprocatingcompressors.

The :petroleum rindustrvin general, and .speci,-- ficall-y the-naturaigas sandgasoline industry uses large-numbers. of. reciprocating or.pistontype. compressors: This. latter. industry.-. uses these.compressors for, among other things; compressing hydrocarbon. gasesprior, to: extraction ofco-ndensible or. gasoline. boiling range: hydro!carbons.:.

Power units for operating sucngascompressors: may beselectedto.o.perateat orvery nearly; capacity-forz maximum operating Aefiiciencyand. for -'savings in capital investment. And further,- these powerunits. may, be. selected to operate at capacity for compressinggasfrom.- an available intake pressure to a.desired ou-tlet pressure;For example;..a compressor. installation. may be designed forcompressing-gasfrom'arnewly drilled: field,. from which. asmal-liamountof gasgmayr-be available: for: compression; at? asrelatively; low pressure. After. the. field is. fully developed; or:the-gas/oil ratio -increases=-the: .pressure .of the gasfrequently.startsLtog-increase. This-increase. field pressure often effects-1amincrease in. pressure in the zsuction-manifoldioia compressor; system;Such-"a: pressureerisesmeans that the compressor; cylinders twill.-receive-, an increased. quantity got? gas on-. each-. intake .l-stroke;If..- the: compressor: is.--v dischargingagainsta constantpressure,;the-;compression .of :this. increased; (1113,11? tit-y: oi.gasswill increase-thee'horsepower demand on the-powerzunit which wasoriginally-operating at its full iratedx p9wer,-. output. This:increased. horsepower; demand: willvthereforegoverload .the: power-unit.

Anothen. compressor installation-.. may; be de signed .-for 1compressinggassfrom. a :newly drilled. field which-is inv a.:flush..period.-of--.productiom. During ,-this initialaperiod theegapressure=.availableeinz-thell suctionemanifold :oi theev compressor-z.installationqmayjbe relatively v-highi. However,,it, isaknownsthatthisgas pressure :Will; decline and. that. .thefieldsmaysubsequentlymroduce at-loweri pressures and over a long period of time.

. stilliother-compressoriinstallationslmay receivegas.:-.at-,-a-.pressure1.which1.may change. from-day; to; day, or.evemfrom hour. tothourr. Most; oil. producing; states; such; asTexasestablish. monthly;- allowable: crude oil. production? for,producing; wells: Under" such circumstances, sems producersfrequently/-pump ..wellsscontim1= ously ot;atgleastieight ahourssazaday: forlthefirst:

. part ofatheimonth o-rluntilthe allowableaoil. hasbeen;.-.produced-.:a:nd. then -.the well. is shutdown duringthe-remainder of" the month. Suchopem ations make for variableproduction .gas pres! sure:

For. any type of gasproduction: compresson cylinders areusuallyyselected so that the power; units :will .be ,fully loaded :when.the compressors-t are operating at-the. expected lower inlet-pressure.Thus it is necessarytoad'just the volue metric efiiciency of thecompressor:cylindersrsor as to load fully but not overload-thepowerunifl during higher pressure production. periods. a

Several methodshaveheretoforebeen available for solving suchanlengineeoverload problem first; installation of. a larger powerengine;- second,- replacement of. .thecompressorlunit with one havingasmaller. cylinder; third; replace-: ment oftheboriginaicompressor.cylinder and piston witha-smaller cylinder and. pistonmwhichlproceduremay-sometimes be followed since many.- compressors g areadapted for such alterations" and fourths installations of externalclearance. pockets, a clearance pocket=being -definedflas an attached,gas receiving: space in direct connection withcthe compressor. cylinder;suchthatsthereeisan increase in residual gasgvolume. atrtheend. of. the.compression. stroke... The. first V two'sof these methods involvesconsiderable. investment whilethe third. involves less, yet appreciable"ex.- pense.. r The H last .method requires. .the "least Vex! penditure;but .its range-- of applicationv is. some! What limited.

Someattempts have been. made. to utilizeaonh and .ofi ormanuallyiadjustable clearancepockets to solve the above I mentioned,problem... Such clearance pockets offer-only aapartial solutionitd theproblemsince an .operatormust recognize the engine: overload. condition.and. then. manuallm open; one-ormore valvesto onea or more clears ancepockets, and this operation to be efie'ctive-l. mustebe done before. annengineestalls ..when=an increasein manifold,gasapressurehas-overloaded: thepower unit. The reverse .is .also' truethat ispan operatormust observe by pressure ga eiorr a recording chartwhen .gas manifold-r pressure: has. decreased, .then .closeofioneor,more clear? ance pockets to, keep; theengine. operating, atmaximunnefficiency. I

An operator of a gas compressionplantlm whichthere gare 12..toZ 15 201.11.10.18 compressors would frequentlyneed .a helper ortwo designated.as clearance pocket-operators? in case .gasmanli; fold pressurefluctuates andzemanuall y, operated" pockets-were i-used.

I have developed a variable and automatically operated clearance pocketfor gas compressors o erating under variable intake pressure conditions.

An object of my invention is to provide an automatically operable meansfor reducing the volumetric efficiency of gas compressors.

Another ob 'ect of my invention is to provide a variable andautomatically operable means for reducing the volumetric efficiency ofgas compressors.

Still another object of my invention is to provide a variable andautomatically operable means for reducing the volumetric efliciency ofgas compressors when compressor suction pressure has become increased,in order to maintain the compression load within the rated power outputof the prime mover driving such compressors.

Man other objects and advantages of my invention will be apparent tothose skilled in the art from a careful study of the followingdisclosure and attached drawing which respectively describes andillustrates a preferred embodiment of my invention.

The figure illustrates diagrammatically, partly in cross section andpartly in elevation, a preferred form of my automatic and variableclearance pocket attached to a compressor cylinder. Referring now to thedrawing, a compressor cylinder I is fitted with a gas inlet pipe 2 and acompressed gas outlet pipe 3. A second connection 4 is provided forattachment of my Variable automatic clearance pocket mechanism 5. Thegasinlet pipe 2 is intended to conduct gas to be compressed from asuction manifold line (not shown) to a compressor cylinder. Pipe 3conducts compressed gas from the compressor cylinder I to a controlchamber 6 of the clearance pocket mechanism; This control chamberdischarges the compressed gas through a pipe 1 which in turn conductsthe compressed gas to a storage tank, to a process step or to otherdisposal, as desired, and not shown on the drawing for purposes ofsimplicity.

My clearance pocket mechanism is composed of two main parts, the controlchamber 6 and a variable clearance section 8.

The variable clearance section 8 is composed of a cylindrical wall 9,the interior surface of which is machined so as to accommodate andpermit movement of a carefully fitted piston [2. A space or volume l6directly under the piston I2 is the variable volume clearancespace. Thiscylindrical wall 8 has a side outlet with a flange I] for connection toflange 4 of the compressor cylinder. The bottom end of the wall 8terminates in a flange l3 to which may be attached a'cover plate I4, theconnection being made gas tight by use of a paper gasket, not shown.Flanges! and l l of course are fitted with gaskets also.

Into the upper end of the piston i2 is inserted byscrew threads or othermeans a connecting rod I5 to the top end of which is attached a conicalshaped bob l6. This bob l6 may be made integral withthe rod l5, ifdesired or may be attached by threads or other means. On account ofrapid movement and vibration during operation it maybe preferable tomake the bob and rod as one unit.

The cylindrical wall 9 is intended to act as a cylinder in which thepiston l2 fitted with one or more piston rings, may move freely.

The upper end of the cylindrical wall 9 has a closure member I! which inturn is fitted with;

a packing gland l8 in such a manner that some oil 20 in the spacebetween the piston and the closure member [1 cannot leak around theconnecting rod IS. A coil spring I9 is attached to the underside of theclosure member I! and to the upper side of the piston l2 or to theconnecting rod H5 at a point near the upper surface of the piston. Thisspring is intended merely to carry the dead weight of the bob, piston,connecting rod and the weight of the oil 20.

A reservoir 25 also contains oil 20 which may pass into or out of thecylinder by way of a tube 26 as the piston l2 falls or rises.

The control chamber 6 is tapered as shown so that the higher the bob I6is in the tapered chamber the greater is the area of the annular spacebetween the periphery of the base of the bob I6 and the side wall of thechamber. The upper end of the chamber 6 is made with an outlet carryinga flange 22 to which a flange of the discharge pipe I may be connected.

My clearance pocket apparatus may be used on substantially any sizecompressor cylinder where clearance pockets are need. The sizes of thepocket cylinder. piston and bob portions may be the same for somedifferent sizes of compressor cylinders, and the control chamber memher6 may be varied in size to suit requirements. That is, a 20 inchdiameter compressor cylinder will. require a larger control sectionmember 6 than will an 18 inch diameter cylinder of the same stroke. The20 inch cylinder will pass a larger volume of gas than an 18 inchcylinder while clearance volume requirements will be of the same orderof magnitude and the volume adjustments for both cylinders may beaccomplished with the use of the same size clearance section 5. Byproviding a flange 24 at the contact between the control section 6 andthe piston section 8 different sizes of control sections 6 may be usedwith one piston section.

A tube 26 connects the bottom of an oil reservoir 25 with the volumebetween the piston l2 and the cylinder closure member IT. This volume,tube 26 and a portion of the reservoir 25 contain the oil 20. A tube 2!establishes fluid communication from the space above the oil inreservoir 25 to the clearance volume I0.

In the operation of my variable automatic clearance pocket, a gas to becompressed may be conveyed to the compressor cylinder at 2 pounds persquare inch gage pressure and compressed to say 50 pounds per squareinch gage pressure. Many gas compressors have spring loaded dischargevalves or such other type of discharge valve that when a predeterminedpressure of the gas is reached the valve will open' and the remainder ofthe compression stroke will then serve to discharge the compressed gas.Under such conditions the engine driving the compressor may be operatingat capacity.

When the pressure of the gas to be compressed is increased to say 5pounds per square inch more power is required to compress gas from thispressure to 50 pounds than from 2 pounds to 50 pounds. Thus the powerengine will be overloaded.

During normal compressor operation the compressed gas passes through thecompressor discharge pipe 3 and passes into and through the controlsection 6 of my apparatus. The surface area of the underside of the bobl6 and the area of the annular space between the bob l6 and the wall ofthe control chamber 6 are so chosen that when this normal volume of gaspasses by asaowca through the annular-space between-bob le and" thiswall of ich'amb'en the-=bob 6- is: exposed :to a; pressure differentialfor a-longen-per-iod of time than 1 when" compressing 1 the one to twopound; gas andthis pressured-i'fieren-tial acting ion b'ob lfi -fo'r'a--'- longer period of 'timewilr move -th'e bob agreaten'distance-in=the d6wnstream d-irec tion" than when the bob -is'exposedts thesame. pressure difierenti-al=-for a--shorter per-iod of time-:

When the bob is raised the-piston-l2 is raised:

also-and 'the volume lfifmore accurately called the"learance volthnegincreases and "this in-- creases-in clearance volumeunloads the drivingengine si-nce it permits discharge of a=smaller= volumeot compressedgas-from the cylinder to the compressor dis-charge pipes in volume ofthedischarged gas is accordingly proportional to theincrease-in clearancevolume. lfi caused by the -rise-of the piston l 2 Y Thetube V 2 Tpermits pressure from withirrthe clearancechamber A W to becommunicatedto the oil 2a. Thus any; pressure acting'on the bottom 'sideof the piston l 2-is-alsoacting-on the top sideof the-piston l2, or inot-h'en-words' the piston is not moved by-"th'e-pressurepf 'gas'-inthe:clearanceyolumei N31: The only force acting to move the piston is thepassage of gas around the bob [6.

The spring I9 need .not be especially strong since it is used merely tosupporttheweight. of the bob-connectingrod-piston assembly and to assistin returningthe bob toitsoriginal and normal position after abnormalinlet gaspres sure has sceasedl to exist...andzthelzvoluine-eofa" aspassingathelb'ob. at. each discharge stroke .issithe normal intendedvolume.

The oil 28 serves as a pulsation dampener. Tube 26 is sized so as toprevent the rapid flow or surging of oil from the cylinder to oilreservoir 25. In some instances it may be desirable to place a choke ororifice in tube 26 to control the fiow of oil. Since the oil isrelatively viscous any movements of the bob are dampened and the overallresult is during times of 2-pound inlet gas pressure the bob remainssubstantially at its initial position, and during times when the inletgas pressure is 5 pounds (or any other pressure greater than 2 pounds)the bob rises and remains substantially fixed at its new position untilthe inlet gas pressure changes. If the gas pressure further increases,the bob will rise further or if the inlet gas pressure drops the bobwill fall also to decrease the clearance volume. In this manner the loadon the engine driving a compressor equipped with the clearance pocket ofmy invention will remain remarkably constant.

The clearance pocket assembly described herein is for one end of acompressor cylinder, and if the compressor is double acting, a similarapparatus may be installed on the other end of the cylinder. It ispreferable to have clearance pocket operation on both ends of such acylinder, otherwise an unbalanced operation results and such unbalancedoperation is not conducive to longer compressor life.

The decrease Th'e diameter: of 'the piston-.- l2; and the-dis ameter'andthe conical pitchuof th'eawalls of the control chamberli relative to thediameterof Y the bob It 'may :be determined :for: each size of"compressor cylinder taking further intov con sideration: the compressorinletand. outlet-press sures. The-diameter :-of the: piston l 2i and"distance of it's-upwardmovementtprovides the in crease incclearancevolumea=- The slope-:onconical pitch, among other factors;determines thedisa tance the bob -rises for-- the passage of a: given volume of gasesthrough a given central chamber. The-smaller the conical pitch, thegreater will be-the bob movement for thepassageof a given,

' volume of gas.-

Theoil used-in the pulsation chamber 25 may be a lubricating oil, asmentioned hereinbefore; and ifalubricating oil it should possess arela-.tively high viscosityindex-z In place of oil, glycerin or-ot-her type-oihydraulicfiuid may be Hsedybutwhatever fluid is used, it should exhibitrelatively-constant characteristics as to viscosity, etc.',, atatmospheric conditions, winter-or summer; as Well"; as at' corn-pressoroperating'temperatures; This fluid should not form sludge nor wax'toplug the;tu-be-2ii-'-or to:interierewith-the movementiof piston; l2'against the-wallet theclearance ch'amber'or with the movement of the rodl5 in the packing gland iii.

If desired and 'to save first cost; the control chamber. may. be maderelatively small'in comparison, to .,the .size ofth'e bob" lfiandthrough this.small,controlfchamber then may be passed alconstantfrjaction offlth'e, compressor output. For example, if theccompressordischarge pip is a A inch. diameter pipe; a. 2 .inch take-off Tpipemaygbe. installed .andjrom. the. ratio of the. ,cross sectionalareasofthese..two ,pipes,.,the smaller should permitfiow. of about. one-fourth.the volume of rcompressedsgas all ofwhich. wouldotherwisemass-throughthe 4, inch pipe. This smallerv volumegofcompressed .gas :then may be. passed .through a relatively; small,control. cham.-.. her to operate;-a .clearance pocket as ereinabovedescribed.

Example,

A compressor cylinder of size 18 inches D' y -ZOF inches is compressinggas at the rate of 1,735 M. C. F. D. (thousand cubic feet per day) froman intake pressure of 2 pounds per square inch gage to a dischargepressure of 43 pounds per square inch gage. Loading is approximatelybrake horsepower. The cylinder clearance is 3.87% atmospheric pressure14.4 pounds per square inch and the n value of the gas is 1.26. Theintake pressure is suddenly increased to 5 pounds gage pressure therebythrowing a compression load of 138 horsepower. on the power unit. Atthis increased intake pressure, the compressor passes gas at the rate of2,070 M. C. F. D. This increased flow of gas actuates the controllingmechanism and increases the clearance volume to 8%, thereby decreasingthe gas flow and unloading the engine to its normal 125 horsepowerloading. At this 8% clearance and '5 pounds inlet gage pressure 1,950 M.C. F. D. of as is passed.

The clearance volume remains at 8% as long as the intake pressure is 5pounds. Upon decrease of intake pressure to 2 pounds, less gas is passedand the apparatus actuates to decrease the clearance volume to 3.87%with an engine loading of 125 brake horsepower.

Materials for use in the construction of my variable automatic clearancepocket may be selected from among those commercially available. Nospecial material is needed.

It will be obvious to those skilled in the art that many variations andmodifications Of my clearance pocket mechanism, such as, dimensions ofmechanical parts, the slope or angle of the side wall of the controlsection, etc., may be made and yet remain within the intended spirit andscope of my invention.

Having disclosed my invention, I claim:

1. A variable, automatic clearance pocket for use in conjunction withreciprocating gas compressors comprising a cylinder adapted to beattached at one end to a compressor cylinder, the first mentionedcylinder fitted with a piston, means to equalize pressure on both sidesof said piston, and means attached to said piston and extending beyondthe other end of its containing cylinder for moving said piston, ahousing means surrounding the extended portion of said piston movingmeans, a further means attached to said housing means and to said gascompressor cylinder and adapted to convey compressed gas from saidcompressor cylinder into said housing means, said extended portion ofsaid piston moving means adapted to move said piston in response to theflow of gas through said housing means.

2. A variable, automatic clearance pocket for use in conjunction withreciprocating gas compressors, comprising a cylinder adapted to beattached at one end to a compressor cylinder having an intake and anoutlet, the first mentioned cylinder fitted with a piston, meansattached to said piston and extending beyond the other end of itscontaining cylinder for moving said piston, and means for equalizingpressure on both sides of said piston, a housing means surrounding theextended portion of said piston moving means, a further means attachedto said housing means and to said gas compressor cylinder and adapted toconvey compressed gas from said compressor cylinder into said housingmeans, said extended portion of said piston moving means adapted to movesaid piston in response to the flow of gas through said housing means.

- 3. The variable, automatic clearance pocket of claim 2 wherein saidmeans for equalizing pressure on both sides of said piston comprisesmeans,

for communicating fluid pressure from one side of said piston to theother side.

4. A'cylinder for a reciprocating gas'compressor having an intake and anoutlet, and means for varying the efiective clearance volume of thecylinder, comprising in combination a clearance volume chamber incommunication at one end with the head of the compressor cylinder, theclearance volume chamber being fitted with a piston to vary theefiective volume of said chamber, a gas flow bob in said outlet andattached to said piston and being responsive to the volume of dischargethrough said outlet to position the piston so that the effective volumeof the clearance chamber will be varied directly as the volume of saiddischarge.

5. A cylinder for a reciprocating gas compressor having an intake and anoutlet, and means for varying the eiTective clearance volume of thecylinder, comprising in combination a clearance volume chamber incommunication at one end with the head of the compressor cylinder, theclearance volume chamber being fitted with a piston to vary theeffective volume of said cham ber, means to equalize pressure onopposite faces of said piston, a gas flow bob in said outlet andattached to said piston and responsive to the volume of dischargethrough said outlet to position said piston so that the effective volumeof the clearance chamber will be Varied directly as the volume of saiddischarge.

CHARLES O. MEYERS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,004,474 Schaer June 11, 19352,121,534 Aikman June 21, 1938

